Constructing Complex Search Queries

Introduction

This page explains how to create and use search expressions on the Expert Search page, and in the search fields, for researching information on BMU CTR. If you are mainly interested in finding a clinical trial to join or learning about the results of a clinical trial, start with the basic search filters on the home page.

Learn about the use of search operators, terms, syntax, and expressions to do an advanced search of the study record data on BMU CTR.

Search expressions consist of a sequence of terms and operators. The operators affect which studies are returned by changing how the search terms are combined or interpreted. Search terms are words or phrases that must appear as values in the study records returned by the search. Search syntax refers to the arrangement of search terms and operators in search expressions used for evaluation by the search engine.

Users can create a search expression on the Expert Search page, which has one search query box, keeps a Search query history of your ten most recent queries (in this browser only), and shows the results underneath. The same syntax also works in every text field of the basic search and of Refine search — all filters (for example, Condition/disease, Other terms, or Location). In a text field, terms without an AREA operator search that field only; on the Expert Search page they search the whole study record.

Search operators

In general, operator precedence (from highest to lowest) is as follows:

1. Search terms and source operators (RANGE)
2. The NOT operator and context operators (AREA)
3. The AND operator
4. The OR operator

The following operator types are described in the sections below:

• Boolean operators
• Grouping operators
• Context operators
• Source operators
• Enumerated fields

Operators must be typed in capital letters (AND, OR, NOT, AREA, RANGE). Lowercase and, or, and not are searched as ordinary words.

Boolean operators

Boolean operators connect search terms and define their logical relationship.

Grouping operators

Grouping operators tell the search engine how to combine the different terms you are using in your search.

Context operators

Context operators control how search terms are evaluated by the search engine and are written using a search parameter inside square brackets without any spaces. BMU CTR has one context operator, AREA, which tells the search engine which area of the BMU CTR database should be searched. Context operators have the same precedence as the NOT operator and apply to the search expression directly to the right of the right square bracket, with no space in between the two.

AREA Tells which search area should be searched. It applies to the word, quoted phrase, or group in parentheses that follows it.

• AREA[InterventionName]aspirin
• AREA[ConditionSearch](asthma OR "chronic obstructive pulmonary disease")
• AREA[BDCTRId]BDCTR-2026-000001

The search areas you can use with AREA are:

Search area names in the same row search the same information.

Source operators

Source operators act like search terms. BMU CTR has one source operator, RANGE, which you can use to find studies within a range of values. Source operators have the same precedence as a search term.

RANGE Finds study records in the search area that have a value greater than or equal to the first parameter (e.g., 2026-01-01) and less than or equal to the second parameter (e.g., MAX). Always put an AREA operator in front of RANGE to say which search area to use.

• Date areas—StartDate, PrimaryCompletionDate, CompletionDate, StudyFirstPostDate, LastUpdatePostDate, and ResultsFirstPostDate. Write dates as YYYY-MM-DD (year, month, day).
• Age areas—MinimumAge and MaximumAge (the youngest and oldest age a participant may be). Write ages as a number of years (for example, 18 or 18 years).

Special RANGE operator values:

• MIN—Use to indicate the smallest value of interest in the current search area.
• MAX—Use to indicate the largest value of interest in the current search area.

Note: The RANGE operator will not find study records with no values in the search area.

• AREA[StartDate]RANGE[2026-01-01, MAX] finds studies that started (or will start) on or after 1 January 2026.
• AREA[ResultsFirstPostDate]RANGE[2026-01-01, 2026-06-30] finds studies whose results were first posted in the first half of 2026.
• AREA[MinimumAge]RANGE[MIN, 12] finds studies that accept participants aged 12 or younger.

Enumerated fields

Some search areas only contain one of a fixed list of values. Use AREA with one of these values to find studies that have it.

For example, AREA[OverallStatus]RECRUITING finds studies that are recruiting, and AREA[Phase]PHASE3 AND AREA[HasResults]true finds Phase 3 studies with posted results.

Operators that are not supported

BMU CTR supports only the operators described on this page. Other operators (for example SEARCH, MISSING, DISTANCE, ALL, or TILT, or operators that control whole-field matching or term expansion) are not supported, and neither are wildcards or searching by distance from a place. There is no synonym or MeSH expansion, and results are not ranked by how well they match (you can sort them by newest, oldest, or title). If you type an operator that is not supported, it is searched as ordinary text, so the search will usually find no studies.

Search terms

Search terms are the words or phrases that will help you find the study records you are interested in. A search term is made up of a word or words that must be part of a clinical study you are looking for. Adding a search operator changes how the search engine uses those search terms to find study records. Using quotation marks around search terms tells the search engine that those words must be found together in that order in a study record for that record to be included in your search results.

• BMU CTR finds study records that contain the text of each term. A term can match part of a longer word (for example, "cardio" also finds "cardiovascular"). Capital and lowercase letters are treated the same.
• There is no synonym expansion, so a search for "heart attack" does not find records that only say "myocardial infarction." Use OR to search for several names at once: "heart attack" OR "myocardial infarction".

Search expressions

A search expression is a sequence of search terms and operators used together by the search engine to find studies you are interested in. The search operators affect the way search terms are 'read' by the search engine and change which studies are found.

Order of precedence among expressions

The order in which different types of search expressions are evaluated by the search engine is shown below from highest to lowest precedence. To increase the precedence of an expression, enclose that expression in parentheses.

1. Search terms, quoted phrases, range expressions, and expressions in parentheses.
2. NOT and AREA, which apply to the expression directly to their right.
3. AND expressions (including terms typed next to each other with no operator).
4. OR expressions.

AND expression

An AND expression consists of a list of one or more terms or expressions, separated by binary Boolean AND operators. If you leave out the operator between two terms, AND is used.

• dizziness AND NOT exhaustion
• dizziness AND NOT exhaustion AND stroke
• breast cancer (the same as breast AND cancer)

The AND operator has the second lowest precedence among search operators. All NOT and AREA expressions are evaluated before the AND expressions formed by connecting them using AND operators.

OR expression

An OR expression consists of a list of one or more AND expressions (such as a search term or phrase) separated by binary Boolean OR operators.

• "heart attack" OR stroke
• "heart attack" OR stroke OR dizziness AND "shortness of breath"

The OR operator has the lowest precedence among search operators. All AND expressions are evaluated before the OR expressions formed by connecting the AND expressions using OR operators. In the second example, a study is found if it mentions a heart attack, or a stroke, or both dizziness and shortness of breath.

More examples

• (diabetes OR "high blood sugar") AND AREA[LocationSearch]Dhaka finds studies about diabetes or high blood sugar with a location in Dhaka.
• AREA[ConditionSearch]tuberculosis AND AREA[OverallStatus]RECRUITING AND AREA[StudyType]INTERVENTIONAL finds recruiting interventional tuberculosis studies.
• AREA[InterventionName]metformin AND AREA[StartDate]RANGE[2026-01-01, MAX] finds studies of metformin that start on or after 1 January 2026.
• dengue AND AREA[MaximumAge]RANGE[MIN, 17] AND AREA[HealthyVolunteers]true finds dengue studies limited to children that accept healthy volunteers.
• AREA[LeadSponsorName]"Bangladesh Medical University" NOT AREA[OverallStatus]WITHDRAWN finds studies led by Bangladesh Medical University that were not withdrawn.

Combining fields and filters

Search expressions can be combined with the other search fields and filters. Every field you fill in is combined — a study must match all of them. Within one filter group (for example, two study phases), a study needs to match any one of the values you tick.

For example, entering "diabetes" in Condition/disease, "metformin" in Intervention/treatment, and ticking Phase 2 and Phase 3 finds studies about diabetes that use metformin and are in Phase 2 or Phase 3.

The More filters menu lets you narrow a search by eligibility criteria, study phase, study type, study results, study documents, funder type, date ranges, more ways to search (title/acronym, outcome measure, sponsor/collaborator, lead sponsor, study IDs, and facility name), and results submitted. To learn more about each filter, see How to Search for Clinical Studies.

Using the address bar

Searches are expressed in the page address, so you can build a query by hand and bookmark or share it. Text parameters accept the search syntax described above (in the address, spaces are written as %20 or +, and quotation marks as %22). The parameters on the search page are (the Expert Search page uses term, sort, view, and page):

The values you can use in aggFilters are:

For example, /search?cond=diabetes&aggFilters=status:rec,studyType:int,phase:2 finds recruiting interventional Phase 2 diabetes studies, and /search?locStr=Sylhet&aggFilters=ages:child finds studies in Sylhet that include children.

More examples:

• /search?intr=aspirin&aggFilters=results:with finds studies of aspirin that have posted results.
• /search?cond=tuberculosis&firstPost=2026-01-01_ finds tuberculosis studies first posted on or after 1 January 2026.
• /search?term=dengue&age=18_65&sort=oldest finds dengue studies that include adults aged 18 to 65, oldest first.
• /search?cond=asthma&locStr=Dhaka&view=map shows asthma studies in Dhaka on the map.
• /expert-search?term=AREA[OverallStatus]RECRUITING%20AND%20AREA[LocationSearch]Khulna runs an Expert Search for recruiting studies with a location in Khulna.